Molecular Sequence Effect on the 13C Carbonyl Chemical Shift Shielding Tensor

The 13C chemical shift tensor of the carboxyl carbon has been determined from the C dipole-coupled chemical shift powder patterns for oxalic acid dihydrate and glycine and for the carbonyl carbon of glycine in the dipeptide glycylalanine and the tripeptide valylglycylalanine. The most shielded component, 33, is found to be perpendicular to the CCO plane for all four compounds, whereas 22 shows variation in magnitude and orientation